A novel spherical adsorbent based on sugarcane bagasse and its preparation method and application

Abstract

The application provides a chitosan-diatomic double-coating assembled bagasse spherical adsorbent and a preparation method and application thereof, and belongs to the adsorption field. The preparation method comprises the following steps: (1) using a citric acid solution as a base body to prepare diatomic suspension liquid; (2) mixing the diatomic suspension liquid obtained in the step (1) with bagasse powder, and then sequentially performing standing and calcination to obtain diatomic single-coating assembled bagasse biochar material; (3) mixing the diatomic single-coating assembled bagasse biochar material obtained in the step (2) with a chitosan solution, and then dropping into a solution to solidify, so that double-coating assembled microspheres are obtained; and (4) mixing the microspheres obtained in the step (3) with a glutaraldehyde solution to perform cross-linking reaction, so that the chitosan-diatomic double-coating assembled bagasse biochar adsorbent is obtained. The adsorbent provided by the application has the advantages of low cost, easy separation and good selective adsorption capacity for platinum group metals.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical adsorption, in particular to a chitosan-diatomic dual-coating assembled bagasse spherical adsorbent and a preparation method and application thereof. BACKGROUND

[0002] Platinum group metals are key materials for new energy and new material industries, and are listed as strategic metals by many countries. Platinum and palladium metal ion chelates have important applications in catalysis, medicine and materials. However, there is a global shortage of platinum group metals, and demand exceeds supply. On the one hand, there are many neglected platinum group metal ions in refinery wastewater that can be recovered and reused, and reasonable and sustainable recovery and utilization is an effective way to solve the current shortage of platinum group metals. On the other hand, excessive platinum group metal ions in water can stimulate the skin, nose and bronchus, and cause runny nose and cough after 2 to 6 months of contact, stimulate the bronchus, and cause severe asthma and breathing difficulties, so it must be recovered and utilized from water bodies.

[0003] At present, the bagasse of sugar factories is usually used for incineration to generate electricity, and the additional value is low. If it can be used for the adsorption of rare and precious metals, significant economic benefits will be generated. After carbonization, the number of available functional groups of bagasse is small, the specific surface area of unprocessed biochar is insufficient, and the reusability is poor, for example, it is difficult to separate from water after adsorption. Therefore, it is of great economic value and social significance to prepare an adsorbent that: 1) can be stably stored in solution and can be easily separated from water; 2) has high adsorption efficiency and good adsorption capacity for platinum metal ions; 3) can achieve selective adsorption of platinum group metals in a multi-ion water body; and 4) is low in cost. SUMMARY

[0004] The present application aims to provide a chitosan-diatomic dual-coating assembled bagasse biochar adsorbent and a preparation method and application thereof. The preparation method of the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent provided by the present application can prepare an adsorbent that can be stably stored in solution and can be easily separated from water after adsorption, has low cost, has good adsorption capacity for platinum metal, and has the ability to selectively adsorb platinum group metal ions.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a chitosan-diatomic dual-coating assembled bagasse biochar adsorbent, comprising the following steps:

[0007] (1) Using a citric acid solution as a base to prepare a diatomic suspension;

[0008] (2) mixing the diatomite suspension obtained in step (1) with bagasse powder, and then sequentially performing standing and calcination to obtain a bagasse biochar material with a diatomite single coating assembled;

[0009] (3) mixing the bagasse biochar material with a diatomite single coating assembled obtained in step (2) with a chitosan gel, and then dropping into a sodium hydroxide solution to solidify, to obtain microspheres;

[0010] (4) mixing the microspheres obtained in step (3) with a glutaraldehyde solution to perform a cross-linking reaction, to obtain a bagasse biochar adsorbent with a chitosan-diatomite double coating assembled.

[0011] Preferably, the particle size of the bagasse powder in step (2) is <0.15 mm.

[0012] Preferably, the mass ratio of the diatomite suspension to the bagasse powder in step (2) is (100-105):(8-10).

[0013] Preferably, the standing time in step (2) is 12 h.

[0014] Preferably, the calcination temperature in step (2) is 500-600 DEG C, and the calcination time is 2-4 h.

[0015] Preferably, the mass ratio of the bagasse biochar material with a diatomite single coating assembled to chitosan in the chitosan solution in step (3) is (0.5-1):(1.8-2).

[0016] Preferably, the content of chitosan in the chitosan solution in step (3) is (0.036-0.5) g / mL.

[0017] Preferably, the solidification solution in step (3) is a NaOH solution; and the concentration of the NaOH solution is 0.45-0.55 mol / L.

[0018] Preferably, the volume content of glutaraldehyde in the glutaraldehyde solution in step (4) is 8-10%.

[0019] Preferably, the mass ratio of the microspheres to the glutaraldehyde solution in step (4) is 5:106.25 g.

[0020] The application provides a bagasse biochar adsorbent with a chitosan-diatomite double coating assembled prepared by the preparation method.

[0021] The application provides an application of the bagasse biochar adsorbent with a chitosan-diatomite double coating assembled in adsorbing platinum group metals.

[0022] The application provides a chitosan-diatomic double-coating assembled bagasse spherical adsorbent and a preparation method and application thereof, and comprises the following steps: (1) adopting a citric acid solution as a base body to prepare diatomic suspension liquid; (2) mixing the diatomic suspension liquid obtained in the step (1) with bagasse powder, and then sequentially performing standing and calcination to obtain diatomic single-coating assembled bagasse biochar material; (3) mixing the diatomic single-coating assembled bagasse biochar material obtained in the step (2) with a chitosan solution, and then dropping into a coagulation solution to obtain double-coating assembled microspheres; and (4) mixing the microspheres obtained in the step (3) with a glutaraldehyde solution to perform cross-linking reaction, so as to obtain the chitosan-diatomic double-coating assembled bagasse biochar adsorbent. The chitosan-diatomic double-coating assembled bagasse biochar adsorbent is prepared by using bagasse as raw material and through double-layer co-burning of the original bagasse biomass and chitosan gel-diatomic suspension liquid. The cellulose and hemicellulose contained in the bagasse provide oxygen-containing groups capable of being combined with platinum group metal ions. The silicon-oxygen bond, hydroxyl bond and amino bond contained in the chitosan-diatomic double-coating assembled layer can all be complexed with the platinum group metal ions, and finally the platinum group metal ions are reduced and adsorbed into the adsorbent. The experimental results show that the chitosan-diatomic double-coating assembled bagasse biochar adsorbent prepared by the preparation method has a maximum single-layer adsorption capacity of 216 mg / g, and has the characteristics of high adsorption efficiency and good adsorption capacity. In addition, the double-coating biochar adsorbent material is low in price, good in stability and easy to separate, and is a new type of adsorbent which can be used for large-scale production and application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A process flow chart for preparing the chitosan-diatomic double-coating assembled bagasse biochar adsorbent in the embodiments of the application;

[0024] Figure 2 An SEM image of the chitosan-diatomic double-coating assembled bagasse biochar adsorbent prepared in Embodiment 1 of the application under 5000 times;

[0025] Figure 3 An SEM image of the chitosan-diatomic double-coating assembled bagasse biochar adsorbent prepared in Embodiment 1 of the application under 50000 times;

[0026] Figure 4 An SEM image of the chitosan-diatomic double-coating assembled bagasse biochar adsorbent prepared in Embodiment 1 of the application after adsorbing metal platinum;

[0027] Figure 5 Pore volume graphs of the chitosan-diatomic double-coating assembled bagasse biochar adsorbent prepared in Embodiment 1 of the application before and after adsorbing metal platinum;

[0028] Figure 6The data graph of the adsorption rate of the chitosan-diatomic earth double-coated assembled bagasse biochar adsorbent prepared in Embodiment 1 of the present application to the solution of platinum group metals in a multi-ion water body. DETAILED DESCRIPTION

[0029] The present application provides a preparation method of a chitosan-diatomic earth double-coated assembled bagasse biochar adsorbent, comprising the following steps:

[0030] (1) using a citric acid solution as a base to prepare a diatomic earth suspension;

[0031] (2) mixing the diatomic earth suspension obtained in the step (1) with bagasse powder, and then sequentially performing standing and calcination to obtain a diatomic earth single-coated assembled bagasse biochar material;

[0032] (3) mixing the diatomic earth single-coated assembled bagasse biochar material obtained in the step (2) with chitosan gel, and then dropping into a sodium hydroxide solution for solidification to obtain microspheres;

[0033] (4) mixing the microspheres obtained in the step (3) with glutaraldehyde solution for cross-linking reaction to obtain the chitosan-diatomic earth double-coated assembled bagasse biochar adsorbent.

[0034] In the present application, the diatomic earth suspension is prepared by an ultrasonic dispersion method.

[0035] In the present application, the specific operation of preparing the diatomic earth suspension by the ultrasonic dispersion method is preferably as follows:

[0036] (a) dissolving citric acid into deionized water to obtain a citric acid solution;

[0037] (b) crushing diatomic earth by a crusher and sieving to obtain diatomic earth powder;

[0038] (c) adding the diatomic earth powder obtained in the step (b) into the citric acid solution obtained in the step (a) for ultrasonic dispersion to obtain a diatomic earth suspension;

[0039] The steps (a) and (b) have no sequence.

[0040] In the present application, the mass ratio of the citric acid particles to the deionized water is preferably (8-15:100-200), more preferably (9-10:100-150), and further preferably (9.12:100). The volume ratio of the citric acid solution to the diatomic earth powder is preferably (108-215):(1-6), more preferably (108-150):(2-4), and further preferably (109:2). The volume ratio of the citric acid solution to the diatomic earth powder is limited in the above range in the present application, which can make the diatomic earth better dispersed under ultrasonic operation.

[0041] After obtaining the diatomite suspension, the diatomite suspension is mixed with the bagasse powder, and then static drying and calcination are sequentially performed to obtain the bagasse biochar material with a diatomite single coating.

[0042] In the present application, the particle size of the bagasse powder is preferably <0.15 mm. By limiting the particle size of the bagasse powder to the above range, the present application can improve the binding capacity of the biomass and the coating, and further improve the adsorption performance of the adsorbent.

[0043] In the present application, the preparation process of the bagasse powder is preferably: the bagasse is sequentially subjected to cleaning, drying, crushing and sieving to obtain the bagasse powder.

[0044] In the present application, the solvent used for cleaning is preferably deionized water; the number of cleaning is preferably three times. The present application does not have special limitations on the cleaning equipment and operation, and the cleaning equipment and operation commonly used by those skilled in the art can be used. By cleaning, the present application can wash away the impurities on the surface of the bagasse.

[0045] In the present application, the temperature of drying is preferably 80℃, and the time of drying is preferably 2 days. The present application does not have special limitations on the drying equipment, and the drying equipment commonly used by those skilled in the art can be used. By drying, the present application can fully remove the water in the bagasse, which is beneficial to the subsequent crushing.

[0046] The present application does not have special limitations on the crushing equipment and operation, and the equipment and operation commonly used by those skilled in the art can be used.

[0047] In the present application, the sieving is preferably 100 mesh sieving. By sieving, the present application can control the particle size of the bagasse powder to be <0.15 mm.

[0048] In the present application, the mass ratio of the diatomite suspension to the bagasse powder is preferably (100-200):(9-13), more preferably (110-150):(9-11), further preferably (110-130):(9.5-10.5), and most preferably (121:10). By limiting the volume of the diatomite suspension to the mass of the bagasse powder to the above range, the present application can better assemble the diatomite coating on the bagasse biochar.

[0049] In the present application, the mixing of the diatomite suspension and the bagasse powder is preferably carried out under stirring; the stirring speed is preferably 150-180 r / min, more preferably 160-170 r / min; the stirring time is preferably 15-25 min, more preferably 20 min. The mixing time of the diatomite suspension and the bagasse powder in the present application is set in the above range, which can fully mix the bagasse powder and the diatomite suspension, and is beneficial to the subsequent assembly of the diatomite coating on the bagasse biochar.

[0050] After the standing is completed, the solution formed by the standing is preferably sequentially subjected to drying and grinding to obtain a dry powder.

[0051] In the present application, the drying temperature is preferably 80-100 DEG C, more preferably 90 DEG C; the drying time is preferably 8-12 h, more preferably 10 h. The present application removes the moisture of the diatomite coating by drying, which is beneficial to the grinding.

[0052] The present application does not have special limitations on the grinding equipment and operation, and the diatomite single-layer coated bagasse material after drying can be ground to a particle size of <0.15 mm.

[0053] In the present application, the calcination is preferably carried out in a muffle furnace; the calcination temperature is preferably 500-700 DEG C, more preferably 600 DEG C; the calcination time is preferably 1-3 h, more preferably 2 h. The present application limits the calcination temperature and time to the above range, which is beneficial to the successful assembly of diatomite and is the optimal firing time for the pores of the material itself, and can make the biochar have a high porosity and improve the adsorption effect of the biochar.

[0054] After the calcination is completed, the present application preferably sequentially subjects the calcination product to cooling, grinding and sieving to obtain a diatomite single-coating assembled bagasse biochar material.

[0055] The present application does not have special limitations on the cooling operation, and the calcination product can be cooled to room temperature.

[0056] The present application does not have special limitations on the grinding equipment and operation, and the operation known to those skilled in the art can be used.

[0057] In the present application, the sieving is preferably 100-mesh sieving. The present application can make the particle size of the diatomite single-coating assembled bagasse biochar material be less than 0.15 mm through sieving, which is beneficial to the subsequent assembly of the double-layer coating of chitosan.

[0058] After obtaining the diatomite single-coating assembled bagasse biochar material, the present application mixes the diatomite single-coating assembled bagasse biochar material with a chitosan solution, and then drops the mixture into a NaOH solution to solidify to obtain microspheres.

[0059] In the present application, the mass ratio of the diatomite single-coated assembled bagasse biochar material to chitosan in the chitosan solution is preferably (1-1.2):(1.8-2), more preferably (1-1.1):(1.9-2), and further preferably 1:2. Limiting the mass ratio of the diatomite single-coated assembled bagasse biochar material to chitosan in the chitosan solution to the above range can ensure the successful assembly of the diatomite single-coated assembled bagasse biochar material and the successful preparation of microspheres.

[0060] In the present application, the solvent in the chitosan solution is preferably acetic acid solution; the volume concentration of the acetic acid solution is preferably 1.5-2.5%, more preferably 2%; the content of chitosan in the chitosan solution is preferably (0.036-0.05) g / mL, more preferably (0.038-0.045) g / mL, and further preferably 0.04 g / mL. Setting the content of chitosan in the chitosan solution to the above range can ensure the sufficient dissolution of chitosan.

[0061] In the present application, the mixing of the diatomite single-coated assembled bagasse biochar material and the chitosan solution is preferably carried out under stirring. The present application does not have a special limitation on the stirring speed, and the skilled person in the art can fully disperse the diatomite single-coated assembled bagasse biochar material in the chitosan solution by using the known operation.

[0062] In the present application, the coagulation solution is preferably NaOH solution; the concentration of the NaOH solution is preferably 0.45-0.55 mol / L, more preferably 0.5 mol / L. Limiting the type and concentration of the coagulation solution to the above range can make the mixed solution form microspheres, and a too high or too low concentration of the NaOH solution can make the liquid droplets become cakes or strips, and cannot obtain a material in the form of microspheres.

[0063] In the present application, the dropping speed of the liquid droplets dropped into the coagulation solution is preferably 0.05 ml / 2-3 s; and the dropping device is preferably a syringe. Controlling the dropping speed to the above range can be conducive to the formation of microspheres.

[0064] The bagasse biochar material with diatomite single-coating assembly is mixed with a chitosan sol, and then is dropped into a NaOH solution to solidify, and the mixed solution of the bagasse biochar material with diatomite single-coating assembly and the chitosan solution forms a gel in the solidification solution, because when the chitosan contacts with the sodium hydroxide, the sodium hydroxide reacts with the amino in the chitosan to generate an ammonium salt, and at the same time, the sodium hydroxide also reacts with the hydroxyl in the chitosan to generate a sodium oxide salt, and these reactions cause the structure of the chitosan molecules to change, so that the chitosan is insoluble in the sodium hydroxide, and the chitosan and the NaOH perform a gelation reaction to form a gel, so that the mixed solution of the bagasse biochar material with diatomite single-coating assembly and the chitosan solution can form microspheres in the solidification solution.

[0065] Preferably, the present application sequentially carries out standing, sieving and cleaning after the dropping is completed to obtain the microspheres.

[0066] In the present application, the standing time is preferably 24 h, and the standing temperature is preferably room temperature. The standing can make the microspheres better solidify.

[0067] The present application does not have special limitations on the equipment and operation of the sieving, and the particle size of the microspheres can be controlled to 900 μm.

[0068] In the present application, the solvent for the cleaning is preferably deionized water, and the present application does not have special limitations on the number of times of cleaning, and the pH of the new cleaning liquid can be neutral.

[0069] After obtaining the microspheres, the present application mixes the microspheres with a glutaraldehyde solution to perform a cross-linking reaction to obtain a chitosan-diatomite double-coating assembled bagasse biochar adsorbent.

[0070] In the present application, the solvent in the glutaraldehyde solution is preferably methanol, and the volume content of the glutaraldehyde in the glutaraldehyde solution is preferably 8-10%, more preferably 8.5-9.5%, and further preferably 9%. Limiting the volume content of the glutaraldehyde to the above range can be beneficial to the cross-linking reaction of the chitosan and the glutaraldehyde in the microspheres, so that the microspheres have the ability to stably exist in acidic and alkaline solutions.

[0071] Preferably, the present application carries out standing after the mixing of the microspheres and the glutaraldehyde solution is completed. The standing of the microspheres in the glutaraldehyde solution can be beneficial to the cross-linking reaction.

[0072] In the present application, the time of the cross-linking reaction is preferably 22-26 h, and more preferably 24 h, and the temperature of the cross-linking reaction is preferably room temperature. The cross-linking reaction can make the surface of the microspheres better link the chitosan bond, and improve the stability of the microspheres in the acidic solution.

[0073] After the cross-linking reaction is completed, the product of the cross-linking reaction is preferably sequentially separated and dried to obtain the sugarcane bagasse biochar material adsorbent coated with chitosan and diatomite.

[0074] In the present application, the separation preferably uses a sieve spoon.

[0075] In the present application, the drying preferably is natural air drying of the separated solid in a culture dish.

[0076] The present application uses sugarcane bagasse as raw material, and prepares biochar from the sugarcane bagasse. The high carbon content and porous characteristics of the biochar, and the large amount of oxygen-containing functional groups in the sugarcane bagasse biochar increase the adsorption rate of platinum ions. Diatomite has unique physical properties such as high permeability, high porosity, small particle size, high adsorption capacity, low thermal conductivity density, and high specific surface area. Chitosan has excellent characteristics such as biocompatibility, biodegradability, abundant resources, inertness, non-toxicity, hydrophilicity, and antibacterial properties. Chitosan has good physical and chemical properties such as chemical stability, excellent chelation performance, high reactivity, and groups that can bind to metal ions. The chitosan-diatomite double-coated sugarcane bagasse biochar greatly increases the groups that can bind to platinum group metal ions and the specific surface area of the adsorbent, improves the adsorption efficiency and adsorption capacity of the adsorbent for platinum group metal ions, and enables the adsorbent to stably exist in the solution. The microsphere adsorbent prepared by the present application can selectively adsorb platinum group metals in water containing multiple ions, and has the ability to enrich noble metals in battery negative electrode materials and catalysts.

[0077] The present application also provides the chitosan-diatomite double-coated sugarcane bagasse biochar adsorbent prepared by the preparation method described in the above technical solution.

[0078] The present application uses chitosan and diatomite double-layer assembly, which greatly increases the groups that can bind to platinum group metal ions and the specific surface area of the adsorbent, improves the adsorption efficiency and adsorption capacity of the adsorbent for platinum group metal ions.

[0079] The present application also provides the application of the chitosan-diatomite double-coated sugarcane bagasse biochar adsorbent in adsorbing platinum ions.

[0080] In the embodiments of the present application, as shown in Figure 1 The preparation process of the chitosan-diatomite double-coated sugarcane bagasse biochar adsorbent is as follows:

[0081] After the waste sugarcane bagasse is washed and dried in an 80℃ oven, impurity-free sugarcane bagasse is obtained. The impurity-free sugarcane bagasse is crushed and sieved to obtain sugarcane bagasse powder.

[0082] The diatomite is added into a citric acid solution to form a suspension, and then bagasse powder is added to obtain a mixed solution. After centrifugation, the solid is ground and then calcined in a muffle furnace, and then ground after being cooled to room temperature to obtain a diatomite single-coating assembled bagasse biochar material;

[0083] The diatomite single-coating assembled bagasse biochar material is mixed with a chitosan solution (chitosan is dissolved in ethanol), and then treated with a NaOH solution and a glutaraldehyde solution (methanol + glutaraldehyde) to obtain a chitosan-diatomite double-coating assembled bagasse biochar material.

[0084] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0085] Embodiment 1

[0086] A preparation method of a chitosan-diatomite double-layer assembled bagasse biochar adsorbent, comprising the following steps:

[0087] (1) A diatomite suspension is prepared by using an ultrasonic dispersion method with a citric acid solution as a base;

[0088] (2) The diatomite suspension obtained in the step (1) is mixed with bagasse powder, and then stirred at a speed of 180 r / min for 20 min. After standing for 12 h, the mixture is dried at 80℃ for 12 h. After drying, the mixture is ground and then passed through a 100-mesh sieve to obtain a dry gel. The dry gel is calcined at 600℃ for 2 h, and then ground after being cooled to room temperature. The ground powder is passed through a 100-mesh sieve to obtain a diatomite single-coating assembled bagasse biochar material. The particle size of the ground powder is less than 0.15 mm. The mass ratio of the diatomite suspension to the bagasse powder is 121:10;

[0089] (3) The diatomite single-coating assembled bagasse biochar material obtained in the step (2) is mixed with a chitosan solution, and then added dropwise into a 0.5 mol / L NaOH solution at a speed of 0.05 mL / 2 s by using a syringe. The mixture is left to stand in the NaOH solution for 24 h. After standing, the mixture is sieved by using a sieve spoon. The sieved microspheres are washed with deionized water until the pH of the washing liquid is neutral to obtain microspheres. The solvent in the chitosan solution is an acetic acid solution. The volume concentration of the acetic acid solution is 2%. The content of chitosan in the chitosan solution is 0.04 g / mL, which is the mass of chitosan to the volume of the acetic acid solution. The mass ratio of the diatomite single-coating assembled bagasse biochar material to chitosan is 1:2;

[0090] (4) mixing the microspheres obtained in step (3) with glutaraldehyde solution, and then standing for 24 hours to perform cross-linking reaction, and then separating by a strainer spoon, and then naturally air-drying the product after the cross-linking reaction in a culture dish to obtain the sugarcane bagasse biochar adsorbent assembled by the double coating of chitosan and diatomite; the solvent in the glutaraldehyde solution is methanol; the volume content of glutaraldehyde in the glutaraldehyde solution is 9%;

[0091] The specific operation of preparing the diatomite suspension by the ultrasonic dispersion method is preferably as follows:

[0092] (a) dissolving 9.21 g of citric acid into 100 ml of deionized water to obtain a citric acid solution;

[0093] (b) crushing the diatomite by a crusher and sieving to obtain diatomite powder;

[0094] (c) adding the diatomite powder obtained in step (b) into the citric acid solution obtained in step (a) to perform ultrasonic dispersion to obtain a diatomite suspension;

[0095] The steps (a) and (b) have no sequence.

[0096] The preparation process of the sugarcane bagasse powder is as follows: washing the sugarcane bagasse with deionized water for three times, drying at 80℃ for 2 days, crushing and sieving through a 100-mesh sieve to obtain the sugarcane bagasse powder.

[0097] The scanning electron microscope (SEM) image of the chitosan-diatomite double-coating assembled sugarcane bagasse biochar adsorbent prepared in Example 1 at 5000 times is shown in Figure 2 From Figure 2 which it can be seen that the prepared chitosan-diatomite double-coating assembled sugarcane bagasse biochar adsorbent material is spherical with a diameter of about 80 μm.

[0098] The scanning electron microscope (SEM) image of the chitosan-diatomite double-coating assembled sugarcane bagasse biochar adsorbent prepared in Example 1 at 50000 times is shown in Figure 3 From Figure 3 which it can be seen that the surface of the prepared chitosan-diatomite double-coating assembled sugarcane bagasse biochar adsorbent material is porous, and the holes with different sizes are arranged in layers on the surface of the microspheres, and from the morphology image it can be seen that the adsorbent has a good pore structure.

[0099] The scanning electron microscope (SEM) image of the chitosan-diatomite double-coating assembled sugarcane bagasse biochar adsorbent after adsorbing platinum ions in Example 1 at 50000 times is shown in Figure 4 From Figure 4 which it can be seen that the hole morphology on the surface of the adsorbent disappears after adsorbing platinum ions, and the block accumulation morphology appears on the surface of the adsorbent, which proves the effective adsorption of platinum ions.

[0100] The pore volume diagrams of the sugarcane bagasse biochar adsorbent assembled with a chitosan-diatomite double coating prepared in Example 1 before and after adsorbing platinum ions are shown below. Figure 5 As shown. From Figure 5 As can be seen, the average pore size distribution of the microsphere adsorbent is 3.0–5.4 nm, indicating the mesoporous nature of the prepared chitosan-diatomaceous earth double-coated sugarcane bagasse biochar adsorbent. The pore volume values ​​of the material after adsorbing platinum ions are significantly reduced, because platinum ions are adsorbed on the adsorbent during the adsorption process, occupying adsorption pore sites.

[0101] The graph shows the adsorption rate of platinum group metals in multi-ion water bodies using the chitosan-diatomaceous earth double-coated sugarcane bagasse biochar adsorbent prepared in Example 1. Figure 6 As can be seen, the microsphere adsorbent can selectively adsorb platinum ions and palladium ions in platinum group metals under water conditions where multiple ions coexist, with adsorption rates of 80% and 83.6%, respectively.

[0102] Practical Example 2

[0103] A method for preparing a chitosan-diatomaceous earth bilayer assembled sugarcane bagasse biochar adsorbent comprises the following steps:

[0104] (1) A diatomaceous earth suspension was prepared using citric acid solution as the matrix;

[0105] (2) The diatomaceous earth suspension obtained in step (1) is mixed with sugarcane bagasse powder and stirred at 180 r / min for 20 min. After standing for 12 h, it is dried at 80℃ for 12 h. After drying, it is ground and passed through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining a dry gel. The obtained dry gel is calcined at 400℃ for 2 h and then cooled to room temperature and ground and passed through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining sugarcane bagasse biochar material assembled with a single coating of diatomaceous earth; the mass ratio of the diatomaceous earth suspension to the sugarcane bagasse powder is 121:10.

[0106] (3) The sugarcane bagasse biochar material assembled with diatomaceous earth single coating obtained in step (2) is mixed with chitosan solution and then added dropwise to 0.5 mol / L NaOH solution at a rate of 0.05 mL / 2 s using a syringe. The mixture is left to stand in NaOH solution for 24 h. After standing, the mixture is sieved with a sieve spoon. The sieved microspheres are then rinsed with deionized water until the pH of the washing solution is neutral to obtain microspheres. The solvent in the chitosan solution is acetic acid solution. The volume concentration of the acetic acid solution is 2%. The chitosan content in the chitosan solution is 0.04 g / mL by mass to volume ratio of acetic acid solution. The mass ratio of sugarcane bagasse biochar material assembled with diatomaceous earth single coating to chitosan is 1:2.

[0107] (4) mixing the microspheres obtained in step (3) with glutaraldehyde solution, and then standing for 24 hours to perform cross-linking reaction, and then separating with a sieve spoon, and then naturally air-drying the product after the cross-linking reaction in a culture dish to obtain a sugarcane bagasse biochar adsorbent assembled by a chitosan-diatomic earth double coating layer; the solvent in the glutaraldehyde solution is methanol; the volume content of glutaraldehyde in the glutaraldehyde solution is 9%;

[0108] The specific operation of preparing the diatomic earth suspension by the ultrasonic dispersion method is preferably as follows:

[0109] (a) dissolving 9.21 g of citric acid into 100 ml of deionized water to obtain a citric acid solution;

[0110] (b) crushing diatomic earth by a crusher and sieving to obtain diatomic earth powder;

[0111] (c) adding the diatomic earth powder obtained in step (b) into the citric acid solution obtained in step (a) dropwise to perform ultrasonic dispersion to obtain a diatomic earth suspension;

[0112] The steps (a) and (b) have no sequence.

[0113] Actual example 3

[0114] A preparation method of a chitosan-diatomic earth double-layer assembled sugarcane bagasse biochar adsorbent, which comprises the following steps:

[0115] (1) using a citric acid solution as a base body to prepare a diatomic earth suspension;

[0116] (2) mixing the diatomic earth suspension obtained in step (1) with sugarcane bagasse powder, and then stirring at a rotating speed of 180 r / min for 20 min, standing for 12 h, and then drying at 80℃ for 12 h, and then grinding and sieving through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, and then calcining the obtained xerogel at 600℃ for 1 h, and then cooling to room temperature and grinding, and then sieving through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, to obtain a diatomic earth single-coating layer assembled sugarcane bagasse biochar material; the mass ratio of the diatomic earth suspension to the sugarcane bagasse powder is 121:10;

[0117] (3) the bagasse biochar material with diatomite single-coating assembly obtained in the step (2) is mixed with a chitosan solution, and then is added dropwise into a 0.5 mol / L NaOH solution at a speed of 0.05 mL / 2 s by using a syringe, and is left to stand in the NaOH solution for 24 h, and then is sieved by using a sieve spoon, and the microspheres after sieving are washed by using deionized water until the pH of the washing liquid is neutral, to obtain microspheres; the solvent in the chitosan solution is an acetic acid solution; the volume concentration of the acetic acid solution is 2%; the content of chitosan in the chitosan solution is 0.04 g / mL in terms of the mass of chitosan to the volume of the acetic acid solution; and the mass ratio of the bagasse biochar material with diatomite single-coating assembly to chitosan is 1:2;

[0118] (4) the microspheres obtained in the step (3) are mixed with a glutaraldehyde solution, and are left to stand for 24 h to perform a cross-linking reaction, and then are separated by using a sieve spoon, and the product after the cross-linking reaction is naturally air-dried in a culture dish, to obtain a bagasse biochar adsorbent with chitosan-diatomite double-coating assembly; the solvent in the glutaraldehyde solution is methanol; and the volume content of glutaraldehyde in the glutaraldehyde solution is 9%;

[0119] The specific operation of preparing the diatomite suspension by using the ultrasonic dispersion method is preferably as follows:

[0120] (a) 9.21 g of citric acid is dissolved into 100 ml of deionized water to obtain a citric acid solution;

[0121] (b) diatomite is crushed by using a crusher and is sieved to obtain diatomite powder;

[0122] (c) the diatomite powder obtained in the step (b) is added dropwise into the citric acid solution obtained in the step (a) to perform ultrasonic dispersion, to obtain a diatomite suspension;

[0123] The steps (a) and (b) have no sequence.

[0124] Actual Example 1, Actual Example 2 and Actual Example 3

[0125] 50 mg of the bagasse biochar adsorbent with chitosan-diatomite double-coating assembly prepared in the Example 1, Actual Example 2 and Actual Example 3 is put into 100 mL of a solution with a platinum ion content of 50 mg / L, and is placed in a water bath constant-temperature oscillator to continuously adsorb for 12 hours at 25°C and 200 r / min, and then is filtered by using a 0.45 um filter head, and the concentration of the platinum ion solution after adsorption is determined by using an atomic absorption spectrometer.

[0126] The three actual cases above all change the process of burning biomass. The equilibrium adsorption rate of the adsorbent prepared by Example 1 to a 50mg / L platinum ion solution reaches 82%, while the equilibrium adsorption rate of the adsorbents prepared by Example 2 and Example 3 to a 50mg / L platinum ion solution only reaches 70% and 65% respectively. The performance difference is due to the difference in the burning temperature and the burning time. The burning temperature of Example 2 is reduced by 200 degrees. The reduction of the temperature weakens the adsorption effect of the material. The reason is that with the increase of the carbonization temperature, the ash content of the biochar increases, the carbon content of the ash-free base increases, and the stability increases. On the contrary, when the temperature is reduced, the formation temperature of the most stable aromatic structure of the biochar is not reached, thus causing the adsorption effect to be reduced. The burning temperature of Example 3 is still 600 degrees, but the burning time is reduced by 1 hour. When the biochar burning time is long enough, the biochar raw materials can be fully carbonized. If the burning time is too short, the carbonization inside the biochar is insufficient, and the pore structure after carbonization is unstable, thus causing the adsorption effect to be reduced. By comparing the three examples, it can be seen that the burning time and temperature of Example 1 are the key factors for the adsorbent to maintain good adsorption effect.

[0127] The scanning electron microscope image of the sugarcane bagasse biochar adsorbent prepared by the chitosan-diatomite double coating assembly of Example 1 after adsorbing platinum ions is shown in Figure 4 From Figure 4 , it can be seen that the surface of the adsorbent changes from the uneven porous structure before adsorption to the surface morphology of the convex block accumulation. The pore volume graph of the chitosan-diatomite double coating assembly of Example 1 before and after adsorbing platinum ions can be seen from Figure 5 , the average pore size distribution of the microspheres adsorbent is 3.0-5.4nm, which indicates that the chitosan-diatomite double coating assembly of the prepared sugarcane bagasse biochar adsorbent has mesoporous properties. The pore volume value of the material after adsorbing platinum ions is significantly reduced, which is due to the platinum ions being adsorbed on the adsorbent during the adsorption process, occupying the adsorption pore sites. The surface morphology and pore volume value show that the chitosan-diatomite double coating assembly of the sugarcane bagasse biochar adsorbent prepared by Example 1 has good adsorption capacity for metal platinum.

[0128] The test on the adsorption performance of the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent prepared in the embodiment 1 shows that the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent has the platinum ion solution concentration of 50 mg / L before adsorption and 9 mg / L after adsorption, and the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent reaches the adsorption equilibrium after 12 hours in the process of adsorbing platinum ions, and the adsorption rate is 82%. Compared with the powder adsorbent, the microsphere adsorbent has a more convenient green recycling method and will not cause the incomplete recycling and secondary pollution of water bodies. The cheap diatomic earth is used to replace the expensive nano silicon dioxide in the application, and the dual-coating assembled spherical adsorbent with low price and excellent performance is prepared. The chitosan-diatomic dual-coating assembled bagasse biochar adsorbent prepared in the embodiment 1 of the application has the final equilibrium adsorption rate of 82% and the maximum monolayer adsorption capacity of 216 mg / g, and has excellent adsorption capacity of noble metal platinum.

[0129] The test on the selective adsorption performance of the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent prepared in the embodiment 1 shows that in the 500 ml multi-ion mixed water body with the platinum, palladium, silver, iron and cadmium ion concentration of 30 mg / L, 50 mg of the chitosan-diatomic dual-coating assembled bagasse biochar adsorbent prepared in the embodiment 1 of the application is put in, and the test result shows that the adsorption rates of the adsorbent on the platinum, palladium, silver, iron and cadmium ions are 80%, 83.6%, 21.4%, 34.6% and 34.2% respectively, and the adsorbent has excellent selective adsorption capacity on platinum group metals.

[0130] The above only describes the preferred embodiments of the application, and it should be noted that the ordinary skilled in the art can make some improvements and refinements without departing from the principles of the application, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A method for preparing a chitosan-diatomic dual-coated assembled bagasse spherical adsorbent, comprising the following steps: (1) preparing a diatomic suspension solution using a citric acid solution as a base; (2) mixing the diatomic suspension solution obtained in step (1) with bagasse powder, and then sequentially performing standing and calcination to obtain a diatomic single-coated assembled bagasse biochar material; (3) mixing the diatomic single-coated assembled bagasse biochar material obtained in step (2) with a chitosan gel, and then dropping into a sodium hydroxide solution for solidification to obtain microspheres; and (4) mixing the microspheres obtained in step (3) with a glutaraldehyde solution for cross-linking reaction to obtain the chitosan-diatomic dual-coated assembled bagasse biochar adsorbent. The particle size of the bagasse powder in step (2) is <0.15 mm. The mass ratio of the diatomic suspension solution to the bagasse powder in step (2) is (100-105) : (8-10). The calcination temperature in step (2) is 500-600℃, and the calcination time is 2-4 h. The mass ratio of the diatomic single-coated assembled bagasse biochar material to chitosan in the chitosan solution in step (3) is (0.5-1) : (1.8-2).

2. The method of claim 1, wherein: The content of chitosan in the chitosan solution in step (3) is (0.036-0.05) g / mL.

3. The method of claim 1, wherein: The solidification solution in step (3) is a NaOH solution, and the concentration of the NaOH solution is 0.45-0.55 mol / L.

4. The method of claim 1, wherein: The volume content of glutaraldehyde in the glutaraldehyde solution in step (4) is 8-10%.

5. The method of claim 1, wherein: 9.The chitosan-diatomic dual-coated assembled bagasse biochar adsorbent prepared by the method of any one of claims 1-8.

6. The method of claim 1, wherein: 10.The application of the chitosan-diatomic dual-coated assembled bagasse biochar adsorbent of claim 9 in adsorbing platinum group metals.

7. The method of claim 1, wherein: ​ 8. The method of claim 1, wherein: ​ ​ ​

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